1. Field of the Invention
The present invention relates to a mobile telephone for conducting telephone service by mounting a subscriber card containing a subscriber's identification code stored as a registered identification code. And more particularly, the present invention relates to a mobile telephone capable of preventing a leakage of private information recorded in the mobile telephone using a subscriber card.
2. Related Background Art
Conventionally, there is an SIM (subscriber identification module) card as a subscriber card inserted into a mobile telephone for mounting when it is used. This SIM card is a memory card having identification information (ID), which is equivalent to a subscriber's telephone number registered in an external memory card for registering a telephone number or the like of a mobile telephone, stored by means of an identification code. Write or read operations to or from the SIM card are under the control of a telephone service company. Therefore, normally it is not expected that the card is used for a purpose of storing some information other than ID.
The main part of the mobile telephone is provided with a slot for mounting the SIM card. After the $IM card is inserted into the slot, a call is enabled and a telephone bill is charged to an owner of the SIM card in this mechanism. Therefore, if you carry the SIM card, you can make a call with a charge to yourself by borrowing someone's telephone, if necessary, without carrying around with your own telephone. On the other hand, you can lend someone else your own telephone with a charge to the person using the telephone.
Conventionally, a mobile telephone using this kind of subscriber card generally has a structure as shown in FIG. 1.
A mobile telephone 110, which is shown, can be used with an SIM card 120 inserted for mounting. The mobile telephone 110 comprises a radio communication section 111, a CPU 112, a RAM/RAM 113, an EEPROM 114, a user interface section 115, and a card mounting section 116 connected to a bus 110.
The radio communication section 111 is used for transmitting/receiving to or from a radio base station (not shown) and modulating/demodulating control signals and voice data via a radio circuit and an antenna. The CPU 112 is a central processing unit built in the mobile telephone 110. The ROM/RAM 113 is a section for storing software for controlling the mobile telephone 110 and also a section for securing a work memory required at executing the software.
The EEPROM 114 is a section for storing private data such as a telephone directory, electronic mails, a schedule, and setting information that the user input from the user interface section 115 and the data is not erased even if the power is turned off. Contents of the recorded and stored data are not affected by the card mounting section 116 or the SIM card 120 described later.
The user interface section 115 comprises a liquid crystal display, buttons, and a speaker attached to the mobile telephone. The card mounting section 116 is used for mounting the SIM card 120 by its insertion.
The SIM card 120 for identifying a registered subscriber is a card for storing an ID equivalent to a telephone number and generally has a built-in IC chip.
The above conventional mobile telephone using a subscriber card, however, has a following problem. That is, if the mobile telephone is lent to anyone else, the private information stored in the mobile telephone leaks out completely to a person using the mobile telephone. The reason is that the private information recorded in an internal memory like the EEPROM is kept to be stored as it is unless it is erased by accessing the information sequentially.